1. Field of the Invention
The present invention relates to a method for driving an address-display separated-type AC (alternating current) plasma display panel and a driving device using the method and more particularly to the method for driving the address-display separated-type AC plasma display panel (PDP) in which display with high definition is made possible and to the driving device using the above method.
The present application claims priority of Japanese Patent Application No. 2003-320461 filed on Sep. 11, 2003, which is hereby incorporated by reference.
2. Description of the Related Art
A plasma display panel (hereinafter may referred simply to as a “PDP”) has, in general, many advantages in that it can be made thin, display on a large screen is made possible with comparative ease, it can provide a wide viewing angle, it can give a quick response, and a like. Therefore, in recent years, the PDP is being widely and increasingly used, as a flat display panel, for wall-hung televisions, public information boards, or a like.
The PDP is roughly classified, depending on its operating method, into two types, one being a DC (Direct Current)-type PDP and another being an AC-type PDP. The DC-type PDP is a PDP whose electrodes are exposed in a discharge space and which is operated in a direct-current discharge state. The AC-type PDP is a PDP whose electrodes are coated with a dielectric layer and are not exposed directly in a discharge gas and which is operated in an alternating-current discharge state. In the DC-type PDP, only while a voltage is being applied, discharge occurs. In the AC-type PDP, discharge is sustained by reversing a polarity of a voltage to be applied. The AC-type PDP is also classified into two types, one being a two-electrode type whose number of electrodes in a display cell is two and another being a three-electrode type whose number of electrodes in the display cell is three.
The three-electrode AC-type PDP will be described below. A plasma display panel 110 of the PDP, as shown in FIG. 18, is so constructed that it has a front substrate 120 and a rear substrate 121, both facing each other and ribs (partition walls) (not shown) are arranged at specified intervals in a matrix form, in a direction being vertical to a surface of a paper for the drawing, between the front substrate 120 and rear substrate 121. The above ribs arranged in the matrix form operate to play a role of providing discharge space 126ij (i=any one of 1, 2, . . . , and m, and j=any one of 1, 2, . . . , and n) and of partitioning display cells 131ij (13124 in FIG. 19). The “m” is equal to the number of horizontal scanning lines making up video signals in one frame and the “n” is equal to the number of pixels making up each of the horizontal scanning lines.
On each region on the front substrate 120 being placed by the rib apart from the rear substrate 121 at a specified interval and being partitioned by the rib are arranged one scanning electrode 122i and one sustaining electrode 123i (see FIG. 18) and on each region on the rear substrate 121 being placed apart from the front substrate 120 and being partitioned by the rib is arranged a data electrode 129j in a manner to be orthogonal to the scanning electrode 122i and sustaining electrode 123i. At each of intersecting points, arranged in a matrix form, where each of the scanning electrodes 122i, each of the sustaining electrodes 123i, and each of the data electrodes 129j intersect one another is formed one display cell 131ij (13124 in FIG. 19) making up the PDP.
A metal layer 132i is stacked on each of the scanning electrodes 122i and each of the sustaining electrodes 123i which are formed on the front substrate 120 made up of a glass substrate or a like (see FIG. 18) and a transparent dielectric layer 124 is stacked all over the metal layer 132i, each of scanning electrode 122i, each of the sustaining electrode 123i and then a protecting layer 125 is stacked on the transparent dielectric layer 124. The metal layer 132i is a layer formed to lower wiring resistance and the protecting layer 125 is a layer made of MgO (magnesium oxide) or a like and to protect the transparent dielectric layer 124 from discharge. On the other hand, a white dielectric layer 128 and a phosphor layer 127 are sequentially stacked all over the data electrodes 129j formed on the rear substrate 121 made up of a glass substrate or a like.
A discharge space 126ij in the three-electrode AC-type PDP 110 having such the configurations as above is filled with a mixed gas of He (helium), Ne (neon), Xe (xenon), and a like in a hermetically sealed manner. As a reference material describing such the conventional three-electrode AC-type PDP, “Society for Information Display 98 Digest” (SID 98 DIGEST) (Page 279 to 281, May, 1998) is available.
Next, configurations of a driving circuit for the conventional three-electrode AC-type PDP 110 are described by referring to FIG. 20. The driving circuit, as shown in FIG. 20, is made up of a scanning driver 134i, a sustaining driver 136, and a data driver 138j (not shown in FIG. 20). The scanning driver 134i applies a voltage described later to scanning electrodes Si (122i in FIG. 18 and S1, S2, . . . , Sm in FIG. 19) in a pre-discharge period 2, scanning period 3, and sustaining period 4 (shown in FIG. 21). The sustaining driver 136 applies a voltage described later to sustaining electrodes Ci (123i in FIG. 18 and C1, C2, . . . , Cm in FIG. 19) in the pre-discharge period 2, scanning period 3, and sustaining period 4. The data driver 138j (not shown) applies a data pulse to data electrodes Dj (129j in FIG. 18 and see FIG. 19) in the scanning period 3. Relations among the pre-discharge period 2, scanning period 3, and sustaining period 4 are as follows. That is, one field during which video signals are applied includes two or more sub-fields, each of which is made up of the pre-discharge period 2, scanning period 3, and sustaining period 4. During each of sub-fields, signals to be applied in one field are applied.
The scanning driver 134i, as shown in FIG. 20, is made up of a pre-discharge power feeding circuit 142 to feed a voltage, in the pre-discharge period 2, to be used for operations of resetting wall charges accumulated on a dielectric layer in the scanning electrode Si and operations of priming discharge, a scanning power feeding circuit 144 to feed a voltage (“Vbw”) to be used to produce a scanning pulse to be applied in synchronization with a data pulse in the scanning period 3, a first power feeding circuit 146 to feed a voltage to be used to produce a sustaining pulse in the sustaining period 4, a pMOS (P-channel Metal Oxide Semiconductor Filed Effect Transistor) Ti1 whose source is connected to a line 147, an nMOS (N-channel MOS FET) Ti2 whose drain is connected to a drain of the nMOS Ti2 and a scanning control circuit 148 (shown in FIG. 20)). A source of the nMOS Ti2 is connected to a terminal of a ground potential GND. A connecting point between the pMOS Ti1 and nMOS Ti2 is connected to the scanning electrode Si. The sustaining driver 136 is made up of a second power feeding circuit 150 to feed a sustaining voltage Vs (C1, C2, . . . , Cm in FIG. 21), a switch Ts, a switch Tg, and a sustaining control circuit 152.
The pre-discharge power feeding circuit 142 is used to reset wall charges accumulated in the sustaining period 4 in a previous sub-field by using a sawtooth-like wave signal to be first applied in the pre-discharge period 2 (see FIG. 21) and to make priming discharge occur by using a sawtooth-like wave signal to be secondly applied in the pre-discharge period 2 and to output a voltage having such voltage waveforms as shown as S1, S2, . . . , Sm in FIG. 21 to be used for adjusting wall charges occurred by the priming discharge by using a sawtooth-like wave signal to be lastly applied in the pre-discharge period 2. The scanning power feeding circuit 144 is made up of a voltage source 145 and a switch Tbw whose one terminal is connected to the voltage source 145 and outputs the voltage “Vbw” from the voltage source 145 in the scanning period 3 to the line 147. The first power feeding circuit 146 outputs a voltage Vs to the line 147 in the sustaining period 4.
The scanning control circuit 148 operates to receive video signals and to feed each of control pulses described below to the pMOS Ti1 and nMOS Ti2. That is, the scanning control circuit 148 feeds a control pulse to turn ON the pMOS Ti1 to a gate of the pMOS Ti1 and a control pulse to turn OFF the nMOS Ti2 to a gate of the nMOS Ti2 in the pre-discharge period 2 during which the three kinds of sawtooth-like wave signals described above are fed from the pre-discharge power feeding circuit 142.
The scanning control circuit 148 feeds, in a period during which a scanning pulse is applied, a control pulse to turn OFF the pMOS Ti1 to a gate of the pMOS Ti1 and a control pulse to turn ON the nMOS Ti2 to a gate of the nMOS Ti2, while it feeds, in the scanning period 3 other than the period during which a scanning pulse is applied, a control pulse to turn ON the pMOS Ti1 to the gate of the pMOS Ti1 and a control pulse to turn OFF the nMOS Ti2 to the gate of the nMOS Ti2.
The scanning control circuit 148 repeats operations, alternately for every half of a period during which a sustaining pulse is applied in the sustaining period 4, that the pMOS Ti1 is turned ON and the nMOS Ti2 is turned OFF in a first half of a period during which a sustaining pulse is being fed and a control pulse to turn OFF the nMOS Ti2 is fed to the gate of the pMOS Ti1 and a control pulse to turn ON the nMOS Ti2 is fed to the gate of the nMOS Ti2 in a second half of the period during which the sustaining pulse is being fed. These operations drive a sustaining driver 149 on a side in which scanning operations are performed.
The sustaining control circuit 152 making up the sustaining driver 136 operates to receive video signals and to feed each of control pulses described below to the pMOS Ti1 and nMOS Ti2. That is, it feeds a control pulse to turn ON a switch Ts to an ON/OFF control inputting port of the switch Ts and a control pulse to turn OFF a switch Tg to an ON/OFF control inputting port of the switch Tg in a period during which a first sawtooth-like wave signal out of the above three kinds of the sawtooth-like signals fed in the pre-discharge period 2 is fed. Then, it also feeds a control pulse to turn OFF the switch Ts to the ON/OFF control inputting port of the switch Ts and a control pulse to turn ON the switch Tg to the ON/OFF control inputting port of the switch Tg in a period during which a second sawtooth-like wave signal is fed. Further, it also feeds a control pulse to turn ON the switch Ts to the ON/OFF control inputting port of the switch Ts and a control pulse to turn OFF the switch Tg to the ON/OFF control inputting port of the switch Tg both in a period during which a last sawtooth-like wave signal is fed and in the scanning period 3.
Also, the sustaining control circuit 152 repeats operations, in the sustaining period 4, alternately during every half period during which a sustaining pulse is being applied, by which a control pulse to turn OFF the switch Ts is fed to the ON/OFF control inputting port of the switch Ts and a control pulse to turn ON the switch Tg is fed to the ON/OFF control inputting port of the switch Tg in a first half of the period during which the sustaining pulse is being fed and a control pulse to turn ON the switch Ts is fed to the ON/OFF control inputting port of the switch Ts and a control pulse to turn OFF the switch Tg is fed to the ON/OFF control inputting port of the switch Tg in a second half of the period during which the sustaining pulse is being fed. One terminal of the switch Ts is connected to the second power feeding circuit 150 and another terminal of the switch Ts is connected to one terminal of the switch Tg. A connecting point between the switch Ts and switch Tg is connected to the sustaining electrode Ci. Another terminal of the switch Tg is connected to a port for a ground potential.
Next, a method for driving the three-electrode address-display separated-type AC PDP 110 having configurations as described above is explained. Now, let it be assumed for explanation that operations during a sub-field 5 start (see FIG. 21). Amounts of wall charges to be formed, by discharge, on a dielectric layer of each electrode in a display cell differ depending on whether or not sustaining discharge has occurred in a sustaining period in a sub-field existing immediately before the sub-field 5. If next writing is done irrespective of such the difference in the amounts of wall charges, occurrence of writing discharge caused by the amounts of wall charges becomes difficult and erroneous writing occurs.
To solve this problem, conventionally, the scanning driver 134i operates to perform initializing (resetting) operations and priming discharge operations in the pre-discharge period 2 in the sub-field 5. That is, the scanning driver 134i turns ON the pMOS Ti1 and turns OFF the nMOS Ti2 to apply a first sawtooth-like wave signal to the scanning electrode Si and the sustaining driver 136 turns ON the switch Ts and OFF the switch Tg from a second half of a period during which a last sustaining pulse fed in the sustaining period 4 in the previous sub-field is being fed. In the period during which the above first sawtooth-like wave signal is being fed to the scanning electrode Si, a voltage Vs is applied to the sustaining electrode Ci and wall charges formed in the sustaining period 1 in the previous sub-field are reset.
Then, the scanning driver 134i turns ON the pMOS Ti1 and OFF the nMOS Ti2 to apply a second sawtooth-like wave signal to the scanning electrode Si, while the sustaining driver 136 turns OFF the switch Ts and ON the switch Tg to apply a ground potential to the sustaining electrode Ci, causing priming discharge to occur. Further, the scanning driver 134i turns ON the pMOS Ti1 and OFF the nMOS Ti2 to apply a last sawtooth-like wave signal to the scanning electrode Si and the sustaining driver 136 turns ON the switch Ts and OFF the switch Tg to apply the voltage Vs to the sustaining electrode Ci in a period during which the above last sawtooth-like wave signal is being applied and in the scanning period 3, thus causing wall charges occurred by priming discharge to be adjusted. The priming discharge operations and wall charge adjusting operations are performed to achieve easy writing of display data to be done in a one-pass scanning manner according to display data, that is, to realize easy occurrence of discharge in a display cell.
When the pre-discharge period 2 described above ends, operations in the scanning period 3 start. From starting time of the scanning period 3, a voltage “Vbw” begins to be output from the voltage source 145 in the scanning driver 134i to the line 147 and to be applied to the scanning electrode Si and, as described above, from starting time of the application of the last sawtooth-like wave signal in the pre-discharge period 2, the voltage “Vs” begins to be applied to the sustaining electrode Ci from the sustaining driver 136. Time of termination of the application of the voltage “Vbw” to be output by the scanning driver 134i to the line 147 is the same as ending time of the scanning period 3 and time of termination of the application of the voltage Vs to be applied by the sustaining driver 136 to the sustaining electrode Ci is the same as ending time of the scanning period 3.
On the other hand, to the gate of the pMOS Ti1 is applied a pulse to turn OFF the pMOS Ti1 from the scanning control circuit 148 with same timing with which display data (pixel data) existing on the i-th scanning line is applied, which makes up video signals fed in one field, for example, display data to be fed to the data electrode Dj is fed and, at the same time, to the gate of the nMOS Ti2 is applied a pulse to turn on the nMOS Ti2 by the scanning control circuit 148 with same timing as described above.
Therefore, while a scanning pulse (see reference number 6 in FIG. 21) is being sequentially applied to the scanning electrodes S1 to Sm (see reference numbers S1 to Sm) in the sub-field 5, n-pieces of data pulse (see reference number 7) in each sub-field is applied to each of the data electrodes (see reference numbers D1 to Dn in FIG. 21) corresponding to each data pulse in the scanning period 3 during which the scanning pulse is being applied to each scanning electrode Si.
In a display cell (in the intersecting portion between the scanning electrode and data electrode) to which data pulse is fed, since a voltage between the scanning electrode Si and the data electrode Dj is boosted and, after the application of the voltage, writing discharge occurs between the scanning electrode Si and data electrode Dj with some time delay (hereinafter called a discharge delay), positive wall charges are formed on a side of the scanning electrode Si. Also, between the sustaining electrode Ci and scanning electrode Si (between surface electrodes) where a large bias is being applied in a potential state at the discharge time, since movements of electric charges occur by an electric field generated between the electrodes, negative wall charges are formed on the sustaining electrode Ci.
Contrary to the above case, in a display cell (pixel) to which a data pulse 7 is not fed, since a voltage between the scanning electrode Si and data electrode Dj is not boosted, writing discharge does not occur and a wall charge change that may occur in such the case where the data pulse 7 is applied does not occur.
Thus, depending on whether or not the data pulse 7 is applied to a display cell, two types of states of wall charges can be made to occur between the scanning electrode Si and sustaining electrode Ci. When these two states of wall charges are made to continue to exist during the subsequent sustaining period 4, display or no-display of the pixel continues. This operation is explained below.
When the application of a scanning pulse 6 to all the scanning electrodes Si (from i=1 to i=m) is terminated, operations in the sustaining period 4 start. A sustaining pulse is applied, by the sustaining driver 149 and sustaining driver 136 on a side where scanning operations are performed, alternately to all the scanning electrodes Si to Sm and all the sustaining electrodes Ci to Cm in a specified period. To the scanning electrode Si is first applied a positive sustaining pulse and then a negative sustaining pulse. The positive sustaining pulse and negative sustaining pulse are alternately applied. To the sustaining electrode Ci is applied a negative sustaining pulse first and then a positive sustaining pulse. The negative sustaining pulse and positive sustaining pulse are alternately applied. A voltage of each of these sustaining pulses is set at a voltage at which discharge (called surface discharge) between a scanning electrode Sk and a sustaining electrode Cl does not start in a display cell 131K1 (“k” is one of 1, 2, . . . , m and “l” is one of 1, 2, . . . , n). More specifically the set voltage is 170 V.
Contrary to the above case, in a display cell 131OP (“O” is one of 1, 2, . . . , m and other than “k” and “P” is one of 1, 2, . . . , n other than “l”) in which writing discharge has occurred, as described above, since a positive wall charge is formed on the scanning electrode SO and a negative wall charge is formed on the sustaining electrode CP, a voltage to be produced by the positive and negative wall charges is superimposed on a voltage of the first positive sustaining pulse (called a “first sustaining pulse”) to be applied to the scanning electrode SO in a forward direction. This causes a voltage exceeding a surface firing voltage to be applied to discharge space 126OP in the display cell 131OP and sustaining discharge occurs between the scanning electrode SO and the sustaining electrode CP. By this sustaining discharge, negative wall charges are accumulated on the scanning electrode SO and positive wall charges on the sustaining electrode CP, which reverses the accumulated state of wall charges.
When the application of the first sustaining pulse is completed, a voltage pulse to be applied to the scanning electrode SO from the sustaining driver 149 on the side where scanning operations are performed and a voltage pulse to be applied to the sustaining electrode CP from the sustaining driver 136 are reversed in phase and each of the phase-reversed voltage pulses (called a “second sustaining pulse”) is applied to the corresponding scanning electrode SO and sustaining electrode CP. A voltage of negative wall charges accumulated on the scanning electrode SO and a voltage of positive wall charges accumulated on the sustaining electrode CP are superimposed on a voltage of the second sustaining pulse to be applied as above in a forward direction and, as in the case of the first sustaining pulse, wall charges having a polarity being reverse to that of a voltage of the first sustaining pulse, that is, positive wall charges are accumulated on the scanning electrode SO and negative wall charges on the sustaining electrode CP.
Even after the application of the second sustaining pulse has been terminated, since the application of the first sustaining pulse and the second sustaining pulse is repeated, discharge continues to occur between the scanning electrode SO and the sustaining electrode CP. That is, a potential difference produced by wall charges formed on the scanning electrode SO and the sustaining electrode CP by the X-th sustaining discharge is superimposed on a voltage of the “X+1st” sustaining pulse, which causes the sustaining discharge to be sustained.
By operating as above, light-emitting in the display cell 131OP continues. Light-emitting luminance in the display cell 131OP is determined by the number of times of sustaining the sustaining discharge. Moreover, by changing the number of sustaining pulses to be applied in each sub-field, gray levels in the display cell 131OP can be adjusted.
A method is disclosed in Japanese Patent Application Laid-open No. Hei 6-337654 in which, in an address-while-display (AWD) driving method in which scanning operations are performed while a sustaining pulse is being applied, after application of a scanning pulse, a pulse having a polarity being reverse to a scanning pulse is applied to an electrode to which a scanning pulse is not applied, out of two surface electrodes. Also, a method is disclosed in Japanese Patent Application Laid-open No. 2001-117532 in which pulse application time is provided between time for application of a scanning pulse and time for application of a subsequent pulse and, during the pulse application time, a pulse having a polarity being reverse to that of the scanning pulse is applied to a sustaining electrode.
In the conventional method for driving the address-display separated-type AC PDP performing such operations as above, when an image with high definition is to be displayed by increasing the number of scanning lines, the scanning period 3 is lengthened as the number of the scanning lines increases. If a frequency to be used in one field is fixed to be 60 Hz, a length of the sustaining period 4 corresponding to an increased length of the scanning period 3 is decreased. The decrease in the length of the sustaining period 4 causes lowering of light-emitting luminance which degrades a display characteristic.
An available countermeasure to avoid the above degradation includes a method by which the number of sub-fields is decreased and another method by which a width of a scanning pulse is decreased. However, the decrease in the number of sub-fields causes a decrease in the number of gray levels or occurrence of false contouring of moving images.
The decrease in a width of a scanning pulse presents the following problems. That is, as is apparent from above descriptions, in the conventional driving method, when application of a scanning pulse is terminated, a potential of the scanning electrode Si is boosted to become a voltage “Vbw”, a potential difference between the scanning electrode Si and sustaining electrode Ci is reduced to be a voltage of “Vs−Vbw”. This means that amounts of movements of space charges which are formed between the scanning electrode Si and sustaining electrode Ci at time of the application of the scanning pulse 6 and which produce wall charges on each of electrodes rapidly becomes small at the same time when the application of the scanning pulse 6 is terminated, which causes further formation of wall charges to be weakened.
That is, since time before the application of the scanning pulse is terminated after writing discharge has started is shortened, formation of wall charges sufficiently enough to let operations in the scanning period 3 shift to have sustaining discharge occur in the sustaining period 4 on the scanning electrode Si and sustaining electrode Ci becomes difficult.
In such the state in which sufficient wall charges are not formed on the scanning electrode Si and sustaining electrode Ci, even if the first sustaining pulse is applied when operations in the sustaining period 4 start and shift to sustaining discharge and even if a voltage of a wall charge formed by the writing discharge is superimposed on the voltage “Vs” of the first sustaining pulse, since the wall charges are not formed sufficiently as described above, a potential difference between the scanning electrode Si and sustaining electrode Ci does not reach a potential difference required for making sustaining discharge occur, that is, does not reach a surface firing voltage being a minimum voltage required for occurrence of surface discharge.
Therefore, unless sufficiently intense discharge occurs before operations start in the sustaining period and unless, when the first sustaining pulse is applied after the occurrence of the intense discharge, a wall charge having a polarity being reverse to that of the wall charge formed by the above discharge is formed on the scanning electrode Si and sustaining electrode Ci, operations do not shift to have sustaining discharge occur with reliability, thus causing a display cell not to be lit or a flicker to occur in displayed images.
To improve points described above, a voltage of a sustaining pulse or of a data pulse has to be boosted. This causes an increase in power consumption and/or use of an expensive driver that can withstand a high voltage, which leads to high costs.
In the address-while-display (AWD) driving method disclosed in Japanese Patent Application Laid-open No. Hei 6-337654 in which scanning operations are performed while a sustaining pulse is being applied, after the application of a scanning pulse, a pulse having a polarity being reverse to that of the scanning pulse is applied to an electrode, out of two surface electrodes, to which the scanning pulse has not been applied. However, simple application of this method to the address-display separated method does not produce a satisfactory effect. To obtain sufficient effects, optimization of a pulse voltage, a position of a pulse to be applied, and a width of the pulse is necessary.
In the method disclosed in Japanese Patent Application Laid-open No. 2001-117532, pulse application time is provided between time for application of a scanning pulse and time for application of a subsequent pulse and, during the pulse application time, a pulse having a polarity being reverse to that of the scanning pulse is applied to a sustaining electrode. Therefore, the pulse application time during which a pulse is applied to a sustaining electrode between time for application of a scanning pulse and time for application of a subsequent pulse is additionally required. As a result, this method enables the scanning pulse to be shortened, however, a scanning period cannot be shortened.